Claims shall be proved by a statement in writing, signed by the creditor or his agent having knowledge of the facts stated, setting forth, under oath, the claim, the consideration therefor, any security held therefor, any payments made or credits that should be allowed thereon and a statement that the claim is justly due from the debtor to the creditor; if the claim is founded upon a writing, the writing shall be attached to the proof unless lost or destroyed. After final allowance or disallowance of the claim, the writing may, by leave of court, be withdrawn and a copy substituted.